The invention relates to a deep hydroprocessing process and, more particularly, to a process for advantageously removing substantial amounts of contaminant such as sulfur from hydrocarbon feedstocks.
A persistent problem in the art of petroleum refining is to reach acceptably low levels of sulfur content and other contaminants.
A large portion of the world""s hydrocarbon reserves contain sulfur, and removal of this sulfur is critical in order to provide acceptable fuels.
Government agencies are currently formulating new regulations which will require sulfur content in fuels to be substantially lower than current practice. It is expected that such regulations will require sulfur content of less than 15 wppm.
A number of processes have been attempted for use in removing sulfur, one of which is hydrodesulfurization, wherein a hydrogen flow is exposed to the feedstock in the presence of a suitable catalyst so that sulfur compounds react to produce a volatile product, hydrogen sulfide.
Such processes do provide substantial reduction in sulfur in the feed. However, existing facilities do not readily provide for reduction of sulfur content to desired levels. Known hydrodesulfurization methods include cocurrent processes, wherein hydrogen and hydrocarbon feed are fed through a reactor or zone in the same direction, and countercurrent processes wherein hydrocarbon is fed in one direction and gas is fed in the other direction.
Known cocurrent processes do not provide acceptable levels of sulfur removal for acceptable catalyst volumes, and countercurrent processes typically experience difficulty in reactor flooding which occurs when the desired amount of gas flow to the reactor prevents flow of the hydrocarbon in the counter direction. Reduction of gas flow to address flooding reduces the effectiveness of countercurrent hydrodesulfurization processes.
Another potential problem with countercurrent processes is that adiabatic countercurrent processes may operate at temperatures much higher than adiabatic cocurrent processes, and this temperature is detrimental to hydrodesulfurization and other catalysts used in the process.
Based upon the foregoing, it is clear that the need remains for an advantageous process for removal of sulfur to levels which will meet the expected regulations on hydrocarbons for use as fuel.
It is therefore the primary object of the present invention to provide a process whereby sulfur content is advantageously reduced to less than or equal to about 10 wppm.
It is a further object of the present invention to provide a process which can be carried out without substantially increasing the equipment size and space occupied by same in current hydrodesulfurization systems.
It is another object of the present invention to provide a hydrodesulfurization system which accomplishes the aforesaid objectives.
It is still another object of the present invention to provide a simple processing scheme that improves sulfur removal as compared to conventional processes.
Other objects and advantages of the present invention will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages have been readily attained.
In accordance with the invention, a process is provided for hydroprocessing a hydrocarbon feedstock with a known flow rate of hydrogen-containing gas and a volume of catalyst, which process comprises the steps of providing a hydrocarbon feed having an initial characteristic; feeding said hydrocarbon feed and a first portion of said hydrogen-containing gas cocurrently to a first hydroprocessing zone containing a first portion of said catalyst so as to provide a first hydrocarbon product; providing an additional hydroprocessing zone containing a remainder of said catalyst; feeding said first hydrocarbon product cocurrently with a remainder of said hydrogen-containing gas to said additional hydroprocessing zone so as to provide a final hydrocarbon product having a final characteristic which is improved as compared to said initial characteristic, wherein said first portion of said hydrogen-containing gas is between about 30 and about 80% vol. of said known flow rate of said hydrogen-containing gas, and said first portion of said catalyst is between about 30 and about 70% wt. of said volume of catalyst.
Still further according to the invention, a system is provided for hydroprocessing a hydrocarbon feed with a known flow rate of hydrogen-containing gas and a volume of hydroprocessing catalyst, which system comprises a first hydroprocessing zone containing a first portion of said hydroprocessing catalyst and having an inlet for cocurrently receiving a hydrocarbon feed and a first portion of said known flow rate of hydrogen-containing gas; and an additional hydroprocessing zone containing a remainder of said hydroprocessing catalyst and having an inlet for cocurrently receiving a hydrocarbon product from said first hydroprocessing zone and a remainder of said hydrogen-containing gas, wherein said first portion of said hydroprocessing catalyst is between about 30 and about 70% wt. of said volume of said hydroprocessing catalyst.
The process and system of the present invention are particularly well suited for use in treating Diesel, gasoil and other distillate feedstocks to reduce sulfur and also for use in treating naphtha and like feedstocks as well, and provide excellent results as compared to conventional processes using a single reactor zone.